Straining Down a Rathole
While Opportunity descends the steep walls of Endurance Crater, it continues to add to its portfolio of evidence on martian water history. Using their rock abrasion tools, otherwise known as "Rat," both of NASA’s Mars Exploration Rovers have dotted the slopes they find to give scientists a glimpse into Mars’ layered geologic history. In soft soil, the rovers can also trench to depths of about six inches by locking five out of six wheels so that the chassis remains stationary and the remaining rotation of one wheel can dig. The depths reachable by this trenching technique however are limited to about one wheel radius before the axle begins to interfere. When traversing down the nearly twenty degree incline of Endurance Crater, the Opportunity rover has purposefully avoided such soft sand and instead is taking breaks to drill directly into the bedrock with the RAT.
The deepest grind performed so far during the mission was previously reported at the Spirit site. That RAT hole drilled 8.12 millimeters (0.32 inches) deep and took two hours and four minutes to create. The previous record was a 7.23-millimeter-deep (0.28-inch-deep) hole dug on sol 86 (April 21, 2004) on the feature dubbed "Pilbara," located in Meridiani’s "Fram Crater".
The observations at the large Endurance Crater indicate that the elements making up the shallow rock layers resemble those of Eagle (where the rover originally came to rest), while the deeper layers of Endurance possess increasingly higher concentrations of the element chlorine. Sulfur content, one key salt-bound element, has proven about the same between the two crater’s exposed histories. When Cornell Principal Investigator, Steve Squyres, first encountered such high sulfur and sulfate proportions inside Eagle Crater, he wrote in his mission diary: "There’s so much sulfur that we think there has to be a lot of some kind of sulfate salt in the rock, which is very hard to account for unless water was involved."
|This view from the Mars Exploration Rover Opportunity’s panoramic camera is an approximately true color rendering of the first seven holes that the rover’s rock abrasion tool dug on the inner slope of "Endurance Crater." The rover was about 12 meters (about 39 feet) down into the crater when it acquired the images combined into this mosaic. The view is looking back toward the rim of the crater, with the rover’s tracks visible. The tailings around the holes drilled by the rock abrasion tool, or "Rat," show evidence for fine-grained red hematite similar to what was observed months earlier in "Eagle Crater" outcrop holes. This image was generated using the panoramic camera’s 750-, 530-, and 430-nanometer filters. It was taken on sol 173 (July 19).
|This view from the Mars Exploration Rover Opportunity’s panoramic camera is a false-color composite rendering of the first seven holes that the rover’s rock abrasion tool dug on the inner slope of "Endurance Crater."
Starting from the uppermost pictured (closest to the crater rim) to the lowest, the rock abrasion tool hole targets are called "Tennessee," "Cobblehill," "Virginia," "London," "Grindstone," "Kettlestone," and "Drammensfjorden." Opportunity drilled these holes on sols 138 (June 13, 2004), 143 (June 18), 145 (June 20), 148 (June 23), 151 (June 26), 153 (June 28) and 161 (July 7), respectively. Each hole is 4.5 centimeters (1.8 inches) in diameter.
Last week, viewers were asked to try seeing as many holes as they could from a black-and-white, navigation-camera image (PIA06716). Most viewers will find it far easier to see the seven holes in this exaggerated color image; the same is true for scientists who are studying the holes from millions of miles away. Credit: NASA/JPL
Related Web Pages
Mars Rovers JPL
Spirit’s images and slideshow
Opportunity image gallery and slideshow
Mars Berries Once Rich in Iron-Water
NASA’s RATs Go Roving on Mars
Pancam– Surveying the Martian Scene
Alpha Proton X-ray Spectrometer